Prior art surface-mount devices include ball grid array (BGA) packages. Ball-grid array packages are surface-mount devices including an integrated circuit (IC) chip and an interposer. The integrated circuit chip is either wire bonded or flip-chip mounted to bond pads on a surface of the interposer. The interposer is generally a small circuit board having bumped solderable pads on the surface of the interposer opposite from the integrated circuit chip. The bond pads and solderable pads of the interposer are electrically connected by metal traces and vias. Solder bumps on the solderable pads serve as interconnects between the interposer and a conductor pattern on a substrate, for example, a printed wiring board (PWB).
For high-speed digital applications, the chip, package (i.e. interposer) and board interconnections of a BGA can exhibit electrical resonances and reflections that degrade signal integrity and electrical system reliability. Such degradations of signal quality are particularly of concern with higher signal frequencies and with digital signals that exhibit shorter rise times. Where low power supply voltages for circuits are employed, electrical resonances and reflections are of great concern because reducing power supply voltages typically requires corresponding reductions in noise levels to avoid detrimental affects on signal integrity.
In the past, discrete termination resistors, in parallel or in series with the signal path, have been employed to eliminate or substantially reduce these resonances and reflections. However, discrete resistors have inherent drawbacks or limitations involving cost, weight, manufacturing complexity, and circuit density. Thus, a need exists for reducing electrical resonances and reflections in high-speed digital applications without sacrificing circuit density or incurring complex manufacturing procedures.